Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk. Accordingly, the movement of the actuator arm allows the transducer to access different tracks. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A conventional hard disk drive (HDD) system, generally designated 10, is illustrated in FIG. 1. The HDD system 10 comprises a data storage disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted to a base plate 16.
The HDD system 10 also includes a drive arm assembly 18, which includes a transducer 20 mounted to a flexure arm 22. As is conventional, the transducer 20 comprises both a write head and a read head. The drive arm assembly 18 is attached to an actuator arm 24 that can rotate about a bearing assembly 26. A drive voice coil motor (VCM) 28 cooperates with the actuator arm 24 and, hence, the drive arm assembly 18, to move the transducer 20 relative to the disk 12.
The spindle motor 14, voice coil motor 28, and transducer 20 are coupled to a number of electronic circuits 30. As will be described in further detail below, the electronic circuits 30 typically include a read channel chip, a microprocessor-based controller, a random access memory (RAM) device, and associated signal drive and logic circuitry.
The disk drive system 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18. However, it is also possible for the disk drive system 10 to include a single disk 12 as shown in FIG. 1. Typically, one drive arm assembly 18 is provided for each surface of each disk 12.
FIG. 2 is a functional block diagram which illustrates a conventional disk drive such as that depicted at 10 in FIG. 1. The example hard disk drive system 10 is coupled to a host device 32 via an input/output 34. The host device 32 may take many forms, including a general purpose computing device, a media player, a cellular telephone, and a digital camera or camcorder.
Data is transferred between the hard disk drive system 10 and a processor of the host device 32 through the input/output port 34. The details of construction and operation of the host device 32 and the input/output port 34 is or may be conventional and will not be described herein beyond the extent necessary for a complete understanding of the present invention.
In addition to the components of the disk drive system 10 shown and labeled in FIG. 1, FIG. 2 illustrates (in block diagram form) that the electronic circuits 30 comprise a drive controller 50, a read/write channel 52, and an interface 54. Conventionally, the drive controller 50 comprises a servo compensator (not shown in FIG. 2). Except as noted below, the details of construction and operation of the drive controller 50, the read/write channel 52, and the interface 54 also are or may be conventional and will not be described herein in further detail.
The disk drive system 10 is used by the host device 32 as a data storage device. The host device 32 delivers data access requests to the disk drive system 10 via the input/output port 34. The data port 34 is used to transfer data between the disk drive system 10 and the host device 32 during read and write operations.
The drive arm assembly 18 is a semi-rigid member that acts as a support structure for the transducer 20, holding it above the surface of the disk 12. The drive arm assembly 18 is coupled at one end to the transducer 20 and at another end to the drive VCM 28. The drive VCM 28 is operative for imparting controlled motion to the actuator arm 18 to appropriately position the transducer 20 with respect to the disk 12. The drive VCM 28 operates in response to a control signal generated by the drive controller 50. The control signal is generated in response to, among other things, an access command received from the host device 32 via the interface 54.
The read/write channel 52 is operative for appropriately processing the data being read from/written to the disk 12. For example, during a read operation, the read/write channel 52 converts an analog read signal generated by the transducer 20 into a digital data signal that can be recognized by the drive controller 50. The channel 52 is also generally capable of recovering timing information from the analog read signal.
During a write operation, the read/write channel 52 converts data received from the host device 32 into a write signal that is delivered to the transducer 20 to “write” the data to an appropriate portion of the disk 12. The read/write channel 52 is also operative for continually processing data read from servo information stored on the disk 12 and delivering the processed data to the drive controller 50 for use in, for example, transducer positioning.
Referring now more specifically to the hard disk 12, as depicted in FIG. 2 the spindle motor 14 is operatively connected to the disk 12 such that the motor 14 rotates the disk 12 relative to the transducer 20. As the spindle motor 14 rotates the disk 12, the transducer 20 stores data on the disk 12 in substantially concentric data storage tracks 60 on a surface 62 of the disk 12. The example data storage disk 12 also includes servo information in the form of a plurality of radially-aligned servo spokes 64 that each cross all of the tracks 60 on the disk 12. The portions of the track between the servo spokes 64 have traditionally been used to store data received from, for example, the host device 32 and are thus referred to herein as data regions 66.
In a magnetic disk drive system 10, data is stored, for example, in the form of magnetic polarity transitions within each track 60. Data is “read” from the disk 12 by positioning the transducer 20 (i.e., the read head) above a desired track 60 of the disk 12 and sensing the magnetic polarity transitions stored within the track 60 as the disk 12 moves below the transducer 20. Similarly, data is “written” to the disk 12 by positioning the transducer 20 (i.e., the write head) above a desired track 60 and delivering a write current representative of the desired data to the transducer 20 at an appropriate time.
The data storage tracks 60 are illustrated as center lines on the surface of the disk 12; however, it should be understood that the actual tracks will each occupy a finite width about a corresponding centerline. It should be understood that, for ease of illustration, only a small number of tracks 60 and servo spokes 64 have been shown on the surface of the disk 12 of FIG. 3. That is, conventional disk drives include one or more disk surfaces having a considerably larger number of tracks and servo spokes.
The servo information in the servo spokes 64 is a specialized form of data stored on the disk 12 that is read by the transducer 20 during disk drive operation for use in positioning the transducer 20 above a desired track 60 of the disk 12. In particular, the disk drive system 10 operates in at least two positioning modes: seek and track following. During the seek mode, the system 10 moves the transducer 20 from an initial track 60a to a target track 60b. During the track following mode, the system 10 maintains the transducer 20 above the desired track 60 while data is read from or written to the disk 12.
The servo information is configured to allow the system 10 to operate in both the seek and track following modes. As is well-known in the art, the servo information stored in the servo spokes allows a servo compensator within the controller 50 to determine a position of the transducer 20 relative to the disk 12. As is conventional, the servo compensator uses the position information during seek and track following modes to move to and/or follow the target track 60b. 
FIG. 2 further shows that the read/write channel 52 comprises a preamplifier circuit 70 and a channel circuit 72. The preamplifier circuit 70 generates the write signal for driving the write head portion of the transducer 20 based on an analog differential drive signal generated by the channel circuit 72. The preamplifier circuit 70 generates an analog playback signal based on a read signal generated by the read head portion of the transducer 20. The playback signal is delivered to the channel circuit 72.
The channel circuit 72 generates the analog differential drive signal based on the digital data to be written to the disk 12. The channel circuit 72 converts the analog playback signal into digital data that can be processed by the drive controller 50 and/or host device 32. The details of construction and operation of the preamplifier circuit 70 and the channel circuit 72 are or may be conventional and will not be described herein in further detail.
A spacing distance between the transducer 20 and the surface 62 of the disk 12 is commonly referred to as “fly height.” The concept of fly height is depicted in FIG. 3, which illustrates in solid lines a position of the transducer 20 at a first example fly height h1 relative to a disk surface and in broken lines a position of the transducer 20 at a second example fly height h2. The second example fly height h2 is less than the first example fly height h1.
As shown in FIG. 3, the transducer 20 comprises a read element 80 and a write element 82 mounted on a head structure 84. The fly height typically varies during normal operation of the disk drive 10. In general, the fly height should be kept at a minimum without allowing the head structure 84 to come into contact with the disk surface 62.
Passive and active systems are employed to control fly height. In particular, FIG. 3 illustrates a component 90 of the head structure 84 commonly referred to as a slider. The slider 90 is a passive component that is aerodynamically designed to create a force on the head structure 84 away from the disk surface 62 when the disk 12 is rotating.
FIG. 3 further illustrates a fly height control driver 92 that applies a fly height control signal to the head structure 84. The head structure 84 comprises a thermal expansion element that expands or contracts under control of the fly height control signal to raise or lower the transducer 20 relative to the head structure 84. By changing a position of the transducer 20 relative to the head structure 84, a distance between the head transducer 20 and the disk surface 62 can be controlled. The fly height control driver 92 operates as part of a fly height control system 94 further comprising the preamplifier circuit 70, the read/write channel circuit 72, and the controller 50.
The construction and operation of the fly height control driver 92 and the head structure 84 is or may be conventional. The construction of the fly height control circuit 94 will be described herein to that extent necessary for a complete understanding of the present invention.
The fly height control circuit 94 causes the fly height control driver 92 to generate the fly height control signal based on the measured spacing between the read element 80 and the disk surface 62. The spacing between the read element 80 and the disk surface 62 can be measured from the read signal generated by the read element 80 under certain conditions. In particular, the read element 80 is arranged adjacent to tracks prewritten with patterns having a suitable harmonic content. The channel circuit 72 generates the current fly height value based on the output of the read element 80 when it passes over these prewritten tracks.
The current fly height value measured as described above is transmitted to the controller 50, which controls the fly height control driver 92 to generate a fly height control signal to eliminate error between the current fly height value and a desired fly height value representative of the preferred spacing between the transducer 20 and a magnetic layer in the disk 12.
Current methods of generating a current fly height value require precise determination of a ratio of the magnitude of harmonics in an “off disk” fly height measurement signal. The applicants have recognized that the accuracy of the measurement of this ratio is highly susceptible to any changes in frequency response in the analog circuitry within the preamplifier circuit 70 and the channel circuit 72.
More specifically, FIG. 4 illustrates the details of an example preamplifier circuit 70 and an example channel circuit 72. The example preamplifier circuit 70 comprises a read first stage amplifier 120, a read second stage amplifier 122, and a write drive circuit 124. The example channel circuit 72 comprises a channel digital signal processor (DSP) 130 and a read portion 132 and a write portion 134. The read portion 132 includes an analog front end (AFE) circuit 140, an analog to digital (A/D) converter 142, and a decode circuit 144. The write portion 134 comprises an encode circuit 150, a serializing circuit 152, and a write precompensator 154.
The inventors have recognized that the analog components within the preamplifier circuit 70 and channel circuit 72 are capable of introducing errors into the calculation of the current fly height value. These analog components include the read second stage amplifier 122 and the analog front end circuit 140 and will be referred to herein as “analog read components.”
In particular, the read element 80 generates the fly height measurement signal while reading tracks prewritten with patterns having a predetermined harmonic content. The read/write channel circuit 72 processes the fly height measurement signal based on ratios of the harmonic content of this signal to determine the current fly height value.
The frequency responses of analog read components, including the read second stage amplifier 122 and the AFE 140, are particularly susceptible to changes based on environmental and implementation factors such as temperature differences and differences in component specifications. Changes in these frequency responses can introduce errors in the fly height control signal that adversely affect the calculation of the current fly height value.
The errors introduced by the analog components of the preamplifier circuit 70 and read/write channel circuit 72 can be significant. For example, bench data suggests that the error incurred by variations in frequency response of the channel AFE 140 alone due to die temperature changes can be as much as approximately 1 nm pole tip protrusion (ptp). Given that the nominal clearance between the head structure 84 and the disk 12 is targeted for 3 nm, the error introduced by the channel AFE 140 can be approximately 30% of the nominal clearance.
The need thus exists for systems and methods for generating current fly height value that are less susceptible to changes in environmental and implementation factors.